Calories burned by exercise = ((METs * 3.5 * weight in kg) / 200) * duration in minutes.
METs
A unit of metabolic equivalent, or MET, is defined as the number of calories consumed by an organism per minute in an activity relative to the Basal metabolic rate (BMR/RMR, see below). A single unit (1 MET) is the caloric consumption of that organism, or individual, while at complete rest. For example, one might consider the restful state following a quiet night’s sleep as a good example of a single MET. This is a base-line unit for that one individual, and since each individual has a varying BMR, a MET is, therefore, variable from one person to the next. One might consider a single unit the energy required to just stay alive without doing anything more.